Under the regulation of some governments, each automobile shall have a triangular warning reflector as an accessory. Furthermore, the size of the triangle is stipulated as a standard specification. The purpose of it is to prevent collision or traffic jam, for safety, by indicating a car in breakdown condition. However, in addition to the triangular reflector which has to meet the standard specification, warning reflector available in the market now is of simple structure for simple application, such as the foldable type which facilitates storing by its folding property. However, all of them are in solid structure made of plastic or metal. Though the application is simple, its prodution cost is rather high, and its cubic measure is bigger (L25.times.W5.times.H3), and must be put in trunk while not in use, therefore, it is inconvenient for timesaving. Nevertheless, a buyer may feel that he has no other choice since he has to comply with the government regulation and buy for safety purpose. This is the inconvenience from the high cost of the reflector due to the limit in structure.